1. Field of the Invention
The present invention relates to a surface light source for allowing a liquid crystal display apparatus to perform narrow view angle display and wide view angle display, and a liquid crystal display apparatus comprising the surface light source.
2. Description of the Related Art
Liquid crystal display devices have a wide view angle. Therefore, there is a risk that the display thereof might be seen by someone other than the viewer from an oblique direction (a direction inclined from the direction of the normal line of the liquid crystal display device).
As a liquid crystal display apparatus which prevents its display from a peeper, there is proposed such a liquid crystal display apparatus in which a view angle limiting device is disposed at one side of the liquid crystal display device for reducing visibility from a direction inclined from the front forward direction of the liquid crystal display device, so that wide view angle display, and narrow view angle display of high security with no risk of peeing by others, are available (Unexamined Japanese Patent Application KOKAI Publication No. 2004-133334).
The view angle limiting device is structured such that a plurality of regions are formed on both of the facing inner surfaces of a pair of substrates, and electrodes having a predetermined shape are formed correspondingly to the respective regions. In each region, liquid crystal molecules of a liquid crystal layer sealed between the pair of substrates are aligned in an alignment state having a view angle in a direction inclined to one side from the direction of the normal line of the liquid crystal display device, and in an alignment state having a view angle in a direction inclined to a side opposite to that side.
This liquid crystal display apparatus limits the view angle of a display image of the liquid crystal display device, by reducing the visibility from an oblique direction by applying a voltage between the electrodes of the view angle limiting device.
That is, when no voltage is applied between the electrodes of the view angle limiting device, i.e., when the view angle limiting device is in a non-display status, the display image of the liquid crystal display device can be seen at a wide view angle. In contrast, when a voltage is applied between the electrodes of the view angle limiting device, there appear displays which correspond to the respective electrodes having the predetermined shape and corresponding to the regions of the view angle limiting device that have a view angle in the direction inclined to one side or corresponding to the regions of the view angle limiting device that have a view angle in the direction inclined to the side opposite to that side, and the display image of the liquid crystal display device is concealed by such displays, when the display image is seen from the direction inclined to one side from the front forward direction and from the direction inclined to the side opposite to that side. Therefore, the display image of the liquid crystal display device becomes unrecognizable from the directions inclined to one side and to the side opposite to that side, and the view angle of the display image is thus seemingly limited, which means that the view angle of the display image is narrowed.
However, the view angle limiting device, in which the liquid crystal molecules are aligned in different alignment states in the respective regions obtained by dividing the area corresponding to the screen of the liquid crystal display device into a plurality of regions, is hard to manufacture, because a complex aligning process (rubbing on aligning films) for imparting different directivities to each region has to be applied to the inner surfaces of the pair of substrates.